guarantor

from WordNet (r) 3.0 (2006)

guarantor
    n 1: one who provides a warrant or guarantee to another [syn:
         {guarantor}, {surety}, {warrantor}, {warranter}]

from The Collaborative International Dictionary of English v.0.48

Guarantor \Guar"an*tor`\, n. [See {Guaranty}, and cf.
   {Warrantor}.] (Law)
      (a) One who makes or gives a guaranty; a warrantor; a
          surety.
      (b) One who engages to secure another in any right or
          possession.
          [1913 Webster]

from Bouvier's Law Dictionary, Revised 6th Ed (1856)

GUARANTOR, contracts. He who makes a guaranty.
     2. The guarantor is bound to fulfill the engagement he has entered into, 
provided the principal debtor does not. He is bound only to the extent that 
the debtor is, and any payment made by the latter, or release of him by the 
creditor, will operate as a release of the guarantor; 3 Penna. R. 19; or 
even if the guarantee should give time to the debtor beyond that contained 
in the agreement, or substitute a new agreement, or do any other act by 
which the guarantor's situation would be worse, the obligation of the latter 
would be discharged. Smith on Mer. Law, 285. 
     3. A guarantor differs from a surety in this, that the former cannot be 
sued until a failure on the part of the principal, when sued; while the 
latter may be sued at the same time with the principal. 10 Watts, 258.

from Moby Thesaurus II by Grady Ward, 1.0

29 Moby Thesaurus words for "guarantor":
      angel, approver, backer, bailsman, bondsman, certifier, confirmer,
      cosignatory, cosigner, endorser, godfather, godparent, guarantee,
      guaranty, insurer, mainpernor, mortgagor, notary, notary public,
      party, patron, ratifier, signatory, sponsor, subscriber, surety,
      underwriter, upholder, warrantor